Shortages of fossil fuel materials in the recent past has spurred much speculation regarding the feasibility of economies based on other energy sources. One such scenario is a hydrogen-fueled economy. Hydrogen has the highest energy density per unit weight of any chemical. Many projections have been made for an economy based on this element, but the technology is not yet in place to effect such a dramatic change in the world economy. Hydrogen is, however, a technically attractive source of fuel and energy storage. It is essentially non-polluting, the major by-product of combustion being H.sub.2 O, and can be made from readily available and abundant raw materials.
While it is well known that hydrogen can be stored as a compressed gas or cryogenically as a liquid, other less energy-intensive and more convenient means are required for widespread utilization of hydrogen as a source of stored energy. It is known that some metals and metal alloys are capable of storing hydrogen reversibly within their lattice. This characteristic may be exploited by exposing the metal or metal alloy to a large pressure of hydrogen, impregnating the metal or metal alloy with hydrogen and later recovering the stored hydrogen by subjecting the impregnated metal or alloy to a change in temperature or pressure.
This characteristic of reversible hydrogen storage for some alloys is also being applied in an electrochemical environment. A metal or metal alloy suitable as a hydrogen storage material may be cathodically biased relative to a suitable counter electrode and charged with hydrogen by the reduction of a proton from solution. Metal alloy systems that have been studied for electrochemical hydrogen storage include LaNi.sub.5 -based, TiMn-based, FeTi-based and Mg-based alloys. Although sone of these crystalline materials store appreciable quantities of hydrogen, these same crystalling materials are susceptible to phase separation, hydrogen embrittlement and surface oxidation when used in charge-discharge cycles for hydrogen storage. Phase separation occurs in crystalline alloys that are subjected to hydrogen cycling, wherein the alloy components separate and migrate throughout the alloy. In LaNi.sub.5 -type alloys, La migrates to the surface of the alloy, where it may rapidly become oxidized.
Hydrogen embrittlement occurs in crystalline alloys as hydrogen is absorbed and desorbed. Hydrogen storage proceeds from the surface of the alloy to its interior, with hydrogen atoms breaking into the interstitial site of metal matrix atoms and then expanding the lattice. As a result internal stresses may produce flaws and cracks, seriously weakening and embrittling the metal or metal alloy. Surface oxidation may occur if the hydrogen storage material is exposed to oxidative conditions in the presence of an oxidant such as CO.sub.2, H.sub.2 O, KOH , air or oxygen. Surface oxidation interferes with the penetration of hydrogen, reducing the amount of hydrogen absorbed and the rate of absorption. Additionally, these crystalline materials generally cannot withstand corrosive environments, which environments may exist when the materials are utilized in an electrochemical reaction.
Recently, amorphous metal alloy materials have been reported as having the ability to store hydrogen reversibly. Amorphous metal alloy materials have become of interest due to their unique combinations of mechanical, chemical and electrical properties. Amorphous metal materials have compositionally variable properties including high hardness and strength, flexibility, soft magnetic and ferroelectronic properties, very high resistance to corrosion and wear, unusual alloy compositions, and high resistance to radiation damage. The unique combinations of properties possessed by amorphous metal alloy materials may be attributed to the disordered atomic structure of amorphous materials that insures that the material is chemically homogeneous and free from the extended defects that are known to limit the performance of crystalline materials.
Amorphous metal alloy systems of TiCu and ZrCu were investigated and contrasted with the absorption properties of the corresponding crystalline intermetallic compounds by Maeland, et al., "Hydrides of Metallic Glass Alloys," Journal of the Less-Common Metals, 74, pp. 279-285, 1980. Amorphous metal alloy compositions, under similar conditions of temperature and pressure were capable of absorbing larger amounts of hydrogen than their crystalline counterparts. Maeland, et al. restricted their studies to the gasous absorption of hydrogen in a hydrogen atmosphere. Novel amorphous metal compositions for reversible hydrogen storage are disclosed in Applicants' co-pending patent application, U.S. Ser. No. 717,429, which disclosure is incorporated herein by reference. This disclosure teaches reversible hydrogen storage materials comprising an amorphous metal alloy of the formula: EQU A.sub.a M.sub.b M'.sub.c
wherein
A is at least one metal selected from the group consisting of Ag, Au, Hg, Pd and Pt; PA0 M is at least one metal selected from the group consisting of Pb, Ru, Cu, Cr, Mo, Si, W, Ni, Al, Sn, Co, Fe, Zn, Cd, Ga and Mn; and PA0 M' is at least one metal selected from the group consisting of Ca, Mg, Ti, Y, Zr, Hf, Nb, V, Ta and the rare earths; and PA0 a ranges from about 0.005 to about 0.80; PA0 b ranges from about 0.05 to about 0.70; and PA0 c ranges from about 0.08 to about 0.95. PA0 A is at least one metal selected from the group consisting of Ag, Au, Hg, Pd and Pt; PA0 M is at least one metal selected from the group consisting of Pb, Ru, Cu, Cr, Mo, Si, W, Ni, Al, Sn, Co, Fe, Zn, Cd, Ga and Mn; and PA0 M' is at least one metal selected from the group consisting of Ca, Mg, Ti, Y, Zr, Hf, Nb, V, Ta and the rare earths; and PA0 a ranges from greater than zero to about 0.80; PA0 b ranges from zero to about 0.70; and PA0 c ranges from about 0.08 to about 0.95; PA0 A is at least one metal selected from the group consisting of Ag, Au, Hg, Pd and Pt; PA0 M is at least one metal selected from the group consisting of Pb, Ru, Cu, Cr, Mo, Si, W, Ni, Al, Sn, Co, Fe, Zn, Cd, Ga and Mn; and PA0 M' is at least one metal selected from the group consisting of Ca, Mg, Ti, Y, Zr, Hf, Nb, V, Ta and the rare earths; and PA0 a ranges from about 0.005 to about 0.80; PA0 b ranges from zero to about 0.70; and PA0 c ranges from about 0.08 to about 0.95; and
wherein
These amorphous compositions are not affected by phase separation or hydrogen embrittlement. Further, the above amorphous compositions have the ability to store from about 0.35 to more than about 1.1 hydrogen atoms per molecule of alloy and do not exhibit any significant signs of surface passivation or corrosion after repeated hydrogen charge/discharge cycles. However, the A component of these compositions is a necessary component of these amorphous alloys, comprising from about one-half to about eighty atomic percent of the alloy, preferably from about ten to about fifty atomic percent and most preferably from about one-half to about forty atomic percent. While the properties of these alloys are ideal for reversible hydrogen storage, their component costs may be prohibitive for widespread applications, especially the A component cost.
Thus it is seen that the potential continues to exist for significant new technological advances in the application of amorphous metal alloys to the development of hydrogen as a fuel and a source of stored energy, especially in the area of electrochemical reversible hydrogen storage. What is needed in this area are economical amorphous metal alloy compositions having the ability to reversibly store hydrogen in significant quantities. Such amorphous metal alloys should not suffer significantly from phase separation or hydrogen-caused embrittlement, nor be susceptible to surface oxidation or corrosion.
It is therefore one object of the present invention to provide economical and improved amorphous metal alloy compositions and structures capable of reversibly storing hydrogen.
It is an additional object of the present invention to provide economical amorphous metal alloy compositions and structures capable of reversibly storing hydrogen in a cyclical fashion without becoming embrittled or suffering from a phase separation.
It is yet another object of the present invention to provide economical amorphous metal alloy compositions and structures capable of reversibly storing hydrogen in a cyclical manner that are not impaired by surface oxidation or corrosion.
These and other objects of the present invention will become obvious to one skilled in the art in the following description of the invention and in the appended claims.